The present invention relates to apparatus and methods for ultrasonic detection of inclusions in molten metals.
Because particulate inclusions in molten metals often have a detrimental effect on metal quality, considerable effort has been devoted in recent years to developing apparatus and methods for detecting such inclusions. Some prior art devices for detecting particulate inclusions in molten metal are described in Young et al U.S. Pat. No. 3,444,726 and Mansfield U.S. Pat. Nos. 4,261,197 and 4,287,755. However, each of these prior art devices suffers from one or more serious limitations making it less than entirely suitable for its intended purpose.
For example, the devices relying upon a probe of titanium metal have a short operating life when used to detect inclusions in molten aluminum because titanium is soluble in aluminum. In addition, solid titanium and other solid metal probes usually contain grain boundaries, gas voids, inclusions and other impurities which may attenuate ultrasonic waves.
Another disadvantage of prior art devices is the need to provide a surface coating on the probe that is wettable by molten metal. Such surface coating causes an attenuation of the ultrasonic signals, thereby interfering with particle analysis.
A further limitation of prior art devices is the need to focus on a reflecting surface. Under production conditions, it is difficult to focus an ultrasonic beam and to maintain a reflective surface at a constant distance from the beam.
It is a principal objective of the present invention to obviate each of the above-mentioned disadvantages in the prior art.
One advantage of the probe described herein is that it is suitable for detecting particles in molten aluminum having a smaller effective particle size than with prior art devices.
Another advantage is that the apparatus and method described herein are suitable for use either with or without focusing a beam of ultrasonic waves. In addition, it is not necessary to have a reflecting surface.
A further advantage of a preferred probe of the invention is that it includes an amorphous silica window that is wetted by molten aluminum.
Additional advantages of the present invention will become apparent to persons skilled in the art from the following specification and drawings.